2018 ASHS Annual Conference

Digital scanning of roots using two-dimensional (2D) scanners or three-dimensional (3D) X-ray computed tomography (CT) are established research techniques. However, CT methodology is lacking in the wide range of substrates used in propagation. The objective was to quantify root growth by 2D or 3D scans for peat, rockwool, and phenolic foam (Oasis^TM) during mist propagation of Euphorbia pulcherrima ‘Prestige Red’ (poinsettia). The experimental design was a randomized block design with two blocks (growth chambers) and two replicate substrate moisture levels (capillary mats) per block. Unrooted cuttings were grown at three constant moisture levels. Three cuttings per treatment combination were harvested on day 14 of propagation. In one experiment, poinsettia were grown in peat (55-mL volume cell) held constant at 53, 58, or 63% volumetric water content (mL water/mL volume). Washed roots were scanned with an image scanner at 800 dpi and analyzed for total root length, surface area, and volume using WinRHIZO^TM. Root growth using 2D imaging did not differ between moisture levels, and averaged 46.3-cm in total length, 13.8-cm² surface area, and 0.34-cm³ volume. In a second experiment, poinsettia were propagated in rockwool or foam. The substrate moisture levels were 11, 19, or 53% volumetric water content for rockwool (45-mL volume) and 18, 34, or 89% for foam (29.7-mL volume). Plants were scanned using nano-CT at 49.8 µm voxel resolution, 1,200 images, and a 20 min. run time. Image segmentation of roots was achieved by drying the substrate down. Root growth was quantified by measuring total surface area, volume, and root count. In rockwool, the high moisture level resulted in a significant increase (p=0.05) in root growth resulting in 760-mm² surface area, 153-mm³ volume, and 19 roots per cutting, relative to moisture levels. Contrast, in foam root growth was similar at 396-mm² surface area, 75-mm³ volume, and 14 roots per cutting across moisture levels. Root growth was also quantified by spacial distribution through image segmentation at 0.5-cm increments from the base of the stem to 2.0-cm depth in plug cells. Root scans by 2D quantified total root growth variables in substrates where roots could be washed. Imaging by CT scans preserves root system architecture in opaque growing media at high resolution and can be quantified for total root growth as well as root spacial distribution.